Regression on extreme values
I don't know of a pre-canned algorithm but I would just sweep on the angle from zero to ninety degrees with a triangular region and count the points.  For each step in the sweep, record the angle and the count.  When the sweep is done you will have an array of angles with bin counts and then you can convert to percentage of total count.  You will have to figure out a resolution of the triangle's angle so that it is fine enough to capture less than 5% of the points.